Nonphotorealistic rendering Feature Edge Advance Computer Graphics Outline
![Silhouette Clipping [Pedro V. Sander et al. 2000]](https://slidetodoc.com/presentation_image_h2/795ebf365bfbd1bef7621884069cb41c/image-21.jpg "Silhouette Clipping [Pedro V. Sander et al. 2000]")
![Suggestive Contours for Conveying Shape [Doug De. Carlo et al. 2003] “Almost contours”: Points](https://slidetodoc.com/presentation_image_h2/795ebf365bfbd1bef7621884069cb41c/image-28.jpg "Suggestive Contours for Conveying Shape [Doug De. Carlo et al. 2003] “Almost contours”: Points")
![Apparent Ridges for Line Drawing [Tilke Judd et al. 2007] The maxima of the](https://slidetodoc.com/presentation_image_h2/795ebf365bfbd1bef7621884069cb41c/image-31.jpg "Apparent Ridges for Line Drawing [Tilke Judd et al. 2007] The maxima of the")
![How Well Do Line Drawings Depict Shape? [Forrester Cole et al. 2009]](https://slidetodoc.com/presentation_image_h2/795ebf365bfbd1bef7621884069cb41c/image-32.jpg "How Well Do Line Drawings Depict Shape? [Forrester Cole et al. 2009]")
- Slides: 32
Non-photorealistic rendering – Feature Edge Advance Computer Graphics
Outline Feature Edge Silhouettes Boundaries Crease
Silhouette detection Real-Time Nonphotorealistic Rendering. Markosian, Kowalski, Trychin, Bourdev, Goldstein, & Hughes. SIGGRAPH 1997.
Applications Visualization Fast, simple “line drawing” style
Observation: silhouette edges are Sparse Connected in long chains Temporally coherent
Definition of a silhouette Normal View vector
Definition of a silhouette N dot V <0: front face N dot V >0: back face N dot V =0: silhouette front face back face
Cusp The vertex is adjacent exactly 2 silhouette edge on front-facing and the other backfacing
More than 2 silhoutte edges
Images space algorithm A B C D X E F G H First order discontinuities G(X) = ( |A + 2 B + C – F - 2 G – H| + |C + 2 E + H – A - 2 D – R|) / 8; Second order discontinuities l = (8 X-A-B-C-D-E-F-G-H)/3
Randomized silhouette detection Check a fraction of edges. Find one, find whole chain Check old silhouettes
Terminology on silhouettes
Silhouette Clipping [Pedro V. Sander et al. 2000]
Definition of a surface boundary It occurs on an non-close model. At least one polygon has at least one edge that is not shared with any other polygon. Cusps: The vertex is adjacent to a boundary edge
Definition of a crease A crease can be define An edge between two front-facing polygons whose dihedral angle theta is above some threshold. C^1 discontinuities
Other Discontinuities
Other Discontinuities
Suggestive Contours for Conveying Shape [Doug De. Carlo et al. 2003] “Almost contours”: Points that become contours in nearby views
Suggestive Contours: Definition 1 Contours in nearby viewpoints (not corresponding to contours in closer views)
Suggestive Contours: Definition 2 n · v not quite zero, but a local minimum (in the projected view direction w)
Apparent Ridges for Line Drawing [Tilke Judd et al. 2007] The maxima of the normal variation with respect to the viewing plane.
How Well Do Line Drawings Depict Shape? [Forrester Cole et al. 2009]